I had similar problem with my old 328. The excess oil is from the engine, the shifter shaft passes through the crankcase and into the trans. Over time the oil from the engine leaks into theThat is just a vent for the trans. Is it overfilled? The drain and fill check are on the back. But there is a fill for the engine transfer gears that might have been overfilled. Has anyone been been servicing it lately?